The present embodiments relate to operating a magnetic resonance apparatus using a safety unit, taking into account persons fitted with implants.
During a magnetic resonance examination, i.e. when Magnetic Resonance Imaging (MRI) is being carried out, for acquisition of magnetic resonance signals by a magnetic resonance apparatus, electromagnetic fields, in particular gradient fields and radio-frequency fields, will usually be employed in accordance with a measurement protocol. To create the gradient fields the magnetic resonance apparatus usually has a gradient coil unit with at least one gradient coil. The magnetic resonance apparatus further mostly has a radio-frequency antenna unit, with which radio-frequency fields can be created for excitation of atomic nuclei.
The gradient fields can cause peripheral nerve stimulations (PNS) and the radio-frequency fields can cause heating. Therefore standardization bodies, such as e.g. IEC 60601-2-33, demand that these PNS and/or heatings will be monitored and restricted. In the past patients fitted with implants were as a rule excluded from a magnetic resonance examination. The development of new, to some extent MR-compatible implants, which can be characterized in accordance with Standard IEC 60601-2-33 by “Fixed Parameter Option: Basic” (FPO:B) makes it possible to allow magnetic resonance examination for persons fitted with implants if specific conditions will be fulfilled.
Typical implants that are to some extent MR-compatible can for example be heart pacemakers, defibrillators and further implants, such as might be used for administration of medication or for deep brain simulation or for stimulation of the spinal column. In an examination of a person fitted with such an implant when applying Standard IEC 60601-2-33, it is to be insured that the magnetic resonance apparatus will be operated in a safe operating mode, in order not to endanger the health of the person fitted with an implant. Usually a condition of the safe operating mode is that there is a restriction of the performance of the magnetic resonance apparatus, so that the safe operating mode can also be referred to as a restricted operating mode. Thus, in accordance with Standard IEC 60601-2-33 in particular, an effective B1+ value B1+rms, a maximum B1+ value B1+peak, an amount of an effective rate of change of a B value (|dB/dt|rms)FPO and an amount of a maximum rate of change (|dB/dt|peak)FPO may not be exceeded.